A hybrid vehicle may recharge an electrical energy storage device during braking, while maintaining vehicle speed down a hill in cruise control, and during pedal off deceleration (e.g., accelerator and brakes not applied) via regenerative braking. In particular, the electrical energy storage device may be recharged by converting the vehicle's kinetic energy into electrical energy by operating an electric machine in a generator mode. However, it may not be possible to convert all of the vehicle's kinetic energy into electrical energy for several reasons. For example, if the electric machine is producing a large amount of current, the electric machine's temperature may increase to a level where the electric machine's current is reduced to lower the possibility of degrading the electric machine. As a result, a portion of the vehicle's kinetic energy may be converted into heat energy by vehicle brakes for the vehicle to follow a desired deceleration rate. The heat energy produced by the vehicle brakes may be lost to the atmosphere, thereby reducing the vehicle's ability to recover and conserve energy.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for cooling a driveline, comprising: operating an electric pump to supply transmission clutches transmission fluid when an engine and an electric machine are stopped; deactivating the electric pump in response to rotation of the engine or the electric machine in response to electric machine temperature less than a threshold; and operating the electric pump while the electric machine is rotating in response to an electric machine temperature exceeding the threshold.
By selectively operating an electric pump, it may be possible to provide the technical result of improved driveline cooling during regenerative braking. Specifically, an electric pump that supplies transmission clutches transmission fluid when a driveline is not being rotated by an engine or electric machine may also be operated when the electric machine is rotating to provide an increased flow rate of transmission fluid to increase electric machine cooling. The electric pump may be operated at the same time as a mechanical pump so that both pumps provide transmission fluid to cool the electric machine during times of increased heat generation by the electric machine. For example, the electric pump may supply transmission fluid to the electric machine when the electric machine is converting the vehicle's kinetic energy into electrical energy.
The present description may provide several advantages. In particular, the approach may improve driveline component cooling. Additionally, the approach may conserve energy when driveline cooling requirements are low and improve driveline cooling when additional driveline cooling may be desired. Further still, the approach may provide additional driveline cooling without additional expense.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.